Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $224.26   4.125%   $233.5107   $233.51   $233.50   $233.50  
  Purchase #2 $77.78   6.102%   $82.5261   $82.53   $82.55   $82.50  
  Purchase #3 $191.52   11.441%   $213.4318   $213.43   $213.45   $213.40  
  Purchase #4 $63.87   10.490%   $70.57   $70.57   $70.55   $70.60  
  Purchase #5 $108.33   4.592%   $113.3045   $113.30   $113.30   $113.30  
  Purchase #6 $187.66   3.428%   $194.093   $194.09   $194.10   $194.10  
  Purchase #7 $133.63   11.424%   $148.8959   $148.90   $148.90   $148.90  
  7 purchase totals = $987.05       $1,056.3320   $1,056.33   $1,056.35   $1,056.30